Shelf unit



FIG. 1 is a perspective view of a shelf unit embodying my new design;

FIG. 2 is a front elevational view thereof;

FIG. 3 is a top plan view thereof;

FIG. 4 is a bottom plan view thereof; and

FIG. 5 is a right side elevational view thereof. 

The ornamental design for a shelf unit, as shown. 